We're going to begin the program tonight in Africa where four U.S. servicemen were injured when their aircraft was fired on while flying over South Sudan. They were there to rescue Americans trapped in South Sudan where a political conflict threatens to escalate into a full-blown civil war.

NPR's Gregory Warner is in Nairobi where the injured soldiers were taken. Greg, what can you tell us about what happened today?

GREGORY WARNER, BYLINE: Sure, Arun. Well, this happened over the city of Bor, which is the capital of Jonglei State in South Sudan. It's in the east of the country. It's on the border of Ethiopia. And that state has really been the site of the most brutal violence over the past week and actually really over the past few years. There's been a lot of ethnic tension there.

So this rescue mission came in three C-22 Ospreys - that's the name of the aircraft. They can hover like a helicopter, but they fly straight like an airplane, so they can do these long flight missions. They're used for resupplying but also rescue operations like this one. They were fired on from the ground with small arms. They aborted the mission. The injured servicemen were first taken to Uganda and then airlifted to Nairobi, one in fairly serious, possibly critical condition.

RATH: Now, this was not a military operation. Like you're saying, it was a rescue mission. Any idea why they would be fired on?

WARNER: Well, look. We don't, of course, know for sure. What we do know is this town is in rebel hands, or you could say hands of the forces that have substantively defected from the South Sudanese army. And as we speak right now, the South Sudanese army is coming in with their ground troops and their attack planes trying to rest back control. So it's possible that the U.S. role was perceived to be more hostile than their mission suggested.

That said, though, it's not like there's any kind of neutrality that's respected in this kind of conflict. In another incident, in the U.N. compound elsewhere in Jonglei State was raided and two U.N. peacekeepers were killed. So, look. The other thing we don't know, of course, is what's the situation for Americans, the Americans that were supposed to be rescued that were not in this remote province. Most likely, they include a lot of humanitarian workers who have been trying to deal with the crisis created by these years of ethnic violence.

So what we're told is that the situation in the town is in crisis mode. People are not moving from their homes. Apparently, soldiers are randomly shooting at civilians. But we should say that the United States and really internationals are not yet a direct target in this conflict.

RATH: It sounds really bad. Is this now a civil war in the making? And what would that mean for the United States?

WARNER: I mean, very briefly, this is not yet a civil war. It's really still seen as a political struggle for power between two men, two of the most powerful politicians in South Sudan. That's President Salva Kiir and then his former vice president, who's now in hiding, Riek Machar. There's a lot of attention to solve this diplomatically, solve it politically if the parties are willing. But, of course, in South Sudan, politics and ethnicity are closely intertwined.

There's a concern that if tit-for-tat attacks keep happening along ethnic lines, that could ignite long-standing divisions and escalate the country into civil war.

RATH: NPR's Gregory Warner. He spoke with us from Nairobi. Greg, thank you.